Magnetic disk device and magnetic head slider

ABSTRACT

A magnetic disk device having a magnetic disk, a magnetic head slider with a magnetic head mounted thereon and having a first surface, a second surface, a third surface and a fourth surface which are formed sequentially from an adjacent side to the magnetic disk, and a gap of a magnetic head arranged on the first surface. A relation of d 1 &lt;d 2 &lt;d 3  is established where d 1  is a depth from the first surface to the second surface, d 2  is a depth from the second surface to the third surface, and d 3  is a depth from the third surface to the fourth surface. The magnetic head slider has a floating pitch attitude of at least 50 micro-radians with respect to the magnetic disk.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 09/761,734, filedJan. 18, 2001, now U.S. Pat. No. 6,556,381, the subject matter of whichis incorporated by reference herein and copending with related U.S.application Ser. No. 10/330,368, filed Dec. 30, 2002, and relates toU.S. application Ser. No. 10/40,904, filed Apr. 23, 2003.

BACKGROUND OF THE INVENTION

This invention relates to a magnetic disk device; and, moreparticularly, the invention relates to the structure of a magnetic headslider and to a magnetic disk in a contact recording magnetic diskdevice in which the magnetic head slider touches the magnetic disk.

To increase the recording density of a magnetic disk device, a narrowingof flying height, that is defined as the spacing between a magnetic headslider mounted with a magnetic head and a rotating magnetic disk, isimportant. A uniform flying height over the entire surface of themagnetic disk is also required. Further, any fluctuation of flyingheight due to environmental changes, especially a decrease of the flyingheight due to a drop in atmospheric pressure when operating at a highaltitude, is required to be minimized. In proportion to a decrease inthe flying height, the possibility of contact by the magnetic headslider with the magnetic disk increases; and, if the degree of contactis severe, the magnetic head slider crashes against the magnetic diskand there is a possibility of destroying the recorded data on themagnetic disk.

A technique for generally equalizing the flying height over the entiresurface of the magnetic disk, for reducing a decrease of the flyingheight and for keeping a uniform flying height all over the magneticdisk when the disk is used at a high altitude, is disclosed byJP-A-2000-57724. This Japanese publication discloses a step air bearingsub-ambient pressure force magnetic head slider which generallyequalizes the flying height over the entire surface of the magnetic diskand makes it possible to reduce a decrease of the flying height when thedisk is used at a high altitude by the adequate combination of the railsurfaces with a step air bearing having a recess with a depth ofsub-microns, the recess being deeper than that of the air bearing, forgenerating a sub-ambient pressure force.

SUMMARY OF THE INVENTION

One way to increase the recording density of a magnetic disk device,while maintaining a high reliability, is to devise measures forpreventing contact between the magnetic head slider and the magneticdisk by narrowing and equalizing the flying height over the entiresurface of the magnetic disk, by reducing fluctuation of the flyingheight caused by the variation of the manufacturing techniques of themagnetic head slider, by reducing fluctuation of the flying heightduring seek operations, and by reducing a decrease of flying height whenthe disk is used at a high altitude.

However, no matter what measures are taken to achieve theabove-described effects, contact between the magnetic head slider andthe magnetic disk is unavoidable with a narrow flying height of 15 nm orless, so that the vibration or the wear on the magnetic head slider arebecoming a new problem.

Regarding the step air bearing sub-ambient pressure force magnetic headslider disclosed in JP-A-2000-57724, it is disclosed that the flyingheight is generally uniform, and that fluctuations in the flying heightdue to variation of the manufacturing tolerances, seek operations anduse in a high altitude environment can be reduced. However, noconsideration is given especially to the vibration of a magnetic headslider caused by contact with the magnetic disk, so that improvement onthis point is needed.

The present invention relates to the above-described needs and intendsto provide a magnetic disk device and a magnetic head slider thatgenerally provide a uniform flying height over the entire surface of themagnetic disk, reduce fluctuations in the flying height due to variationof the manufacturing tolerances, during seek operations and use in ahigh altitude environment, and, in case of contact between the magnetichead slider and the magnetic disk, the magnetic head slider slides onthe surface of the magnetic disk smoothly while maintaining a highreliability.

To solve above described problems, the present invention adopts thefollowing technology.

A magnetic head slider comprising: on the air flow-out side, which isthe closest to the magnetic disk in operation, a magnetic head mountingsurface adjacent to while a magnetic head is mounted; a slider railsurface which is separated from said magnetic head mounting surface andforms a surface near to the air flow-in side, both side surfaces nearthe air flow-in edge having a depth of 10 nm to 50 nm from the magnetichead mounting surface; a slider step air bearing surface formed tosurround said slider rail surface and having a depth of 50 nm to 200 nmfrom said slider rail surface; and a recess for generating a sub-ambientpressure force surrounding said slider step air bearing surface andhaving a depth of 400 nm to 1.3 μm from said slider step air bearingsurface.

A magnetic disk device is provided with the magnetic head slider mountedwith a magnetic head and a magnetic disk that operates as a datarecording medium, wherein the vicinity of said magnetic head of saidmagnetic head slider has the possibility of contacting said magneticdisk in operation, said magnetic head slider having a length of 1.25 mmor less, a width of 1 mm or less and a thickness of 0.3 mm or less, andthe friction force exerted between said magnetic head slider and saidmagnetic disk is 10 mN or less.

A magnetic disk device is provided with a magnetic head slider having amagnetic head and a magnetic disk that operates as a data recordingmedium, wherein the vicinity of said magnetic head of said magnetic headslider has the possibility of contacting said magnetic disk inoperation, the floating pitch angle of said magnetic head slider being50 micro-radian or more, the mean surface roughness Ra of said magneticdisk being 2 nm or less and the peak count thereof being 700/400 μm² ormore.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is the top view of the magnetic head slider representing a firstpreferred embodiment of the present invention.

FIG. 2 is a cross-sectional view taken along line A—A in the FIG. 1.

FIG. 3 is the diagram illustrating the state of contact between themagnetic head slider and the magnetic disk in the first preferredembodiment of the present invention.

FIG. 4 is a graph showing the relation between the friction forcegenerated by the contact between the magnetic head slider and themagnetic disk, and the amplitude of vibration in the first preferredembodiment of the present invention.

FIG. 5 is a graph showing the relation between the pitch attitude angleof the magnetic head slider and the amplitude of vibration in the firstpreferred embodiment of the present invention.

FIG. 6 is a graph showing the relation between the peak count of themagnetic disk and the amplitude of vibration of the magnetic head sliderof the first preferred embodiment of the present invention.

FIG. 7 is a graph showing the floating profiles of the magnetic headslider of the first preferred embodiment of the present invention atground altitude and high altitude.

FIG. 8 is a graph showing the relation between the depth d1 between afirst surface constituting element and a second surface constitutingelement of the magnetic head slider of the first preferred embodiment ofthe present invention, and the amplitude of vibration.

FIG. 9 is a graph showing the relation between the depth d2 between asecond surface constituting element and a third surface constitutingelement of the magnetic head of the first preferred embodiment of thepresent invention, and the ratio of flying heights.

FIG. 10 is a graph showing the relation between the depth 3 between thethird surface constituting element and the fourth surface constitutingelement of the magnetic head slider of the first preferred embodiment ofthe present invention, and the difference of flying heights at groundaltitude and high altitude.

FIG. 11 is a graph showing the relation between the area of the firstsurface constituting element 5 a of the magnetic head slider of thefirst preferred embodiment of the present invention, and the amplitudeof vibration.

FIG. 12 is a process flow diagram illustrating an example of the processof producing a magnetic head slider of the first preferred embodiment ofthe present invention.

FIG. 13 is a top view of the magnetic head slider of a second preferredembodiment of the present invention.

FIG. 14 is a cross-sectional view taken along lien A—A in the directionof arrows in the FIG. 13.

FIG. 15 is a top view of the magnetic head slider of a third preferredembodiment of the present invention.

FIG. 16 is a top view of the magnetic head slider of a fourth preferredembodiment of the present invention.

FIG. 17 is a top view of the magnetic head slider of fifth preferredembodiment of the present invention.

FIG. 18 is a perspective view of a magnetic disk device mounted with aload/unload mechanism provided with the magnetic head slider of thepresent invention.

FIG. 19 is a top view of the magnetic head slider of a sixth preferredembodiment of the present invention.

FIG. 20 is a top view of the magnetic head slider of a seventh preferredembodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description of various embodiments of the magnetic head slider and themagnetic disk device therewith according to the present invention willbe presented with reference to the drawings.

FIG. 1 is a top view of the magnetic head slider of a first preferredembodiment of the present invention. FIG. 2 is the cross section takenalong line A—A in FIG. 1.

As is shown, the magnetic head slider 1 of the first preferredembodiment of the present invention is provided with an air flow-in edge2, an air flow-out edge 3 and a floating surface 4. The floating surface4, facing a magnetic disk which is not shown, is provided with firstsurface constituting elements 5 a, 5 b and 5 c, which form a firstsurface positioned most closely adjacent to the magnetic disk, secondsurface constituting elements 6 a, 6 b and 6 c, which form a secondsurface further separated from the magnetic disk than the first surface,third surface constituting elements 7 a, 7 b and 7 c, which form a thirdsurface even further separated from the magnetic head than the secondsurface, and fourth surface constituting element 8 which forms a fourthsurface most separated from the magnetic disk.

The first to the fourth surfaces are substantially parallel planarsurfaces arranged such that, the depth d1 from the first surfaceconstituting element 5 a to the second surface constituting element 6 ais 30 nm, the depth d2 from the second surface constituting element 6 ato the third surface constituting element 7 a is 120 nm and the depthfrom the third surface constituting element 7 a to the fourth surfaceconstituting element 8 is 800 nm. The magnetic head slider1 has a lengthof 1.25 mm, a width of 1.0 mm and a thickness of 0.3 mm.

The first surface constituting element 5 a is provided with a magnetichead 9. The magnetic head 9 comprises a recording inductive head and areproducing GMR (Giant Magneto-Resistance) head. The recording gap ofthe inductive head and the reproducing gap of GMR are formed on asurface which is substantially in the same plane as the surface of thefirst surface constituting element 5 a.

The term gap refers to either a recording gap or a reproducing gap inthe following discussion. Here, substantially the same surface refers tothe fact that, since the hardness is different among the base material(generally AlTiC) constituting the magnetic head slider 1, theconstituting member of the magnetic head 9 and the protecting member(generally alumina) of the magnetic head, the softer magnetic head willbe abraded to a greater extent in lapping work, thereby forming adifference in level of several nano-meters. This difference of the levelin is not intentional and is clearly different from the other surfacesthat are intentionally formed.

In this preferred embodiment of the invention, a surface provided withthe magnetic head 9 is defined as the first surface, but a protrudingsurface provided for the purpose of preventing sticking at the contactstop of the magnetic head on the magnetic disk can be formed on the sidecloser to the magnetic disk than the first surface.

FIG. 3 is a diagram illustrating the relative positions of a magnetichead slider 1 and a magnetic disk 10 of the above-described firstpreferred embodiment of the present invention operating inside themagnetic disk device.

When an airflow generated by the rotation of the magnetic disk 10 entersbetween the magnetic head slider 1 and the magnetic disk 10, pressure isgenerated between the second surface constituting elements 6 a, 6 b and6 c and the magnetic disk 10, so that the magnetic head slider 1 beginsto float off the surface of the magnetic disk 10. In this preferredembodiment of the present invention, the second surface constitutingelements 6 a, 6 b and 6 c correspond to the rail surfaces of aconventional magnetic head slider of the type which has been widelyused.

The magnetic head slider 1 is generally designed to float with such anattitude that the flying height on the side of the air flow-in edge 2 islarger than the flying height on the side of the air flow-out edge 3.Therefore, the air flow-out edge 3 approaches most closely to themagnetic disk 10.

In the magnetic head slider of the first preferred embodiment of thepresent invention, the first surface constituting element 5 a approachesmost closely to the magnetic disk 10, and in case where the magnetichead slider 1 contacts the magnetic disk 10, the contact occurs at thefirst surface constituting element 5 a, and a friction force is exertedon the contacting surface. The depth d1 from the first surfaceconstituting element 5 a to the second surface constituting element 6 ais 30 nm, so that and the depth d1 is sufficient to limit the contactbetween the magnetic head slider 1 and the magnetic disk 10 to the firstsurface constituting element 5 a. By mounting the magnetic head 9 on thefirst surface constituting element 5 a, the magnetic head 9 approachesthe magnetic disk 10 at the closest point, so that and the recordingdensity can be improved.

The third surface constituting elements 7 a and 7 b are structured tosurround the second surface constituting elements 6 a, 6 b and 6 c. Theairflow, having entered between the magnetic head slider 1 and themagnetic disk 10, is compressed by the third surface constitutingelements 7 a and 7 b, and then enters the second surface constitutingelements 6 a, 6 b and 6 c. The third surface constituting elements 7 aand 7 b correspond to the step air bearing surface or the taperedsurface of the magnetic head that has been widely used. The depth d2from the second surface constituting element to the third surfaceconstituting element is a very important parameter which operates toequalize the flying height over the entire surface of the magnetic disk.This will be described later.

The fourth surface constituting element 8 is surrounded by the thirdsurface constituting element 7 b, and a sub-ambient pressure force isgenerated at the fourth surface constituting element 8 (this sub-ambientpressure force causes the slider to approach the magnetic disk). Thatis, the fourth surface constituting element 8 corresponds to a recessfor a generating sub-ambient pressure force as provided by theconventional magnetic head that has been widely used. The depth d3 fromthe third surface constituting element 7 a to the fourth surfaceconstituting element 8 is very important to reduce a decrease of theflying height caused by an atmospheric pressure drop when operationoccurs in high altitude conditions, and this will be describedafterward.

FIG. 4 shows the relation between the friction force acting between thefirst surface constituting element 5 a of the magnetic head slider 1 andthe magnetic disk 10, and the vibration displacement (FIG. 3, in thedirection of arrow B) of the magnetic head slider 1 in the firstpreferred embodiment of the present invention.

The friction force was measured by a friction sensor comprising a pairof parallel leaf springs and a strain gauge. For measuring the frictionforce with the actual magnetic disk device, for example, the frictionforce can be obtained indirectly by measuring the rotational torque of aspindle motor. For measuring the vibration displacement of the magnetichead slider 1, the velocity variation of the magnetic head slider 1caused by contact in the direction of the arrow B is measured by a laserdoppler vibrometer. The laser doppler vibrometer, model OFV2700 made byPolytec PI Inc. was used with a sampling frequency of 4 MHz. To removethe influence of the run-out frequency of the magnetic disk and theresonant frequency of the suspension, a high-pass filtering process of40 KHz was applied to the data measured by the laser doppler vibrometer.

After the above data processing, the vibration displacement waveform wasobtained by integrating the velocity data with time. The vibrationamplitude shown in FIG. 4 indicates the value of the standard deviationof the vibration displacement waveform after the above signalprocessing. For measuring vibration displacement by contact with theactual magnetic disk device, for example, there is a method of measuringit from the read waveform of the magnetic head 9. When the vibrationdisplacement is larger, jitter that is affected by the vibration in thedirection of bits (peripheral direction) and off-track affected by thevibration in the direction of the track width will become moreconspicuous, and the bit error rate of the magnetic disk device will behigher as a result of it.

As shown in FIG. 4, when the friction force is zero, that is, when themagnetic head slider 1 is floating on the magnetic disk 10 and does notcontact the magnetic disk, a vibration of small amplitude of 0.3 nm isseen (friction is zero on the axis of abscissa in FIG. 4). When theflying height of the magnetic head 1 decreases further and the magnetichead 1 starts to touch the magnetic disk 10, the friction force betweenthem increases. Corresponding to the increase of the friction force, thevibration amplitude increases gradually.

In case the friction force increases, if the moment by the frictionforce around pivots (supporting points that support the slider) issufficiently smaller than the moment formed around the pivots by theforce of the air flowing between the magnetic head slider and themagnetic disk, the magnetic head slider runs in contact with themagnetic disk stably, the increase of the vibration amplitude is smallin spite of the contact, and according to the experimental result, thevibration amplitude is approximately 1 nm when the friction force is notmore than 10 mN. In such a range where the friction force is not morethan 10 mN, a similar bit error rate can be obtained relative to thoseobtained with a floating magnetic head. However, when the friction forceexceeds 10 mN, the moment around the pivots by the friction force isequivalent to or more than the moment around the pivots by the airpressure, so that the vibration amplitude increases drastically. In sucha region of the friction force, the magnetic head 9 cannot record orreproduce data on the magnetic disk 10 and the bit error rate increasessuddenly.

With the preferred embodiment of the present invention, the frictionforce at which the vibration amplitude increases suddenly is 10 mN, butthis critical friction force is considered to depend on the shape of themagnetic head slider. The magnetic head slider 1 of the preferredembodiment of the present invention has, as above described, the shallowdepth 3 of the fourth surface constituting element 8 that generates asub-ambient pressure force that is 900 nm, and, therefore, a sliderwhich is 1.25 mm in length, 1.0 mm in width and 0.3 mm in thicknessgenerates a very large sub-ambient pressure force of 30 mN for its size.Further, the magnetic head slider 1 contacts the magnetic disk 10 withthe first surface constituting element 5 a having small area, and thesecond, third and fourth surfaces are separated far from the magneticdisk 10; therefore, there is a an advantage in that the contactingsurface is limited to the first surface constituting element 5 a.

The magnetic head slider 1 of the preferred embodiment of the presentinvention comprises the structure provided with the above-described area(especially, the first surface constituting element 5 a is set small)and the depth.

Considering these, when a magnetic head slider having a differentconfiguration than the magnetic head slider 1 of the preferredembodiment of the present invention is used, the critical friction forceis thought to be less than 10 mN. This means that the stable contactarea is narrow, and this is not desirable from the point of view of thereliability of the magnetic disk device.

FIG. 5 is a diagram showing the relation between the pitch attitudeangle Θ and the vibration amplitude. The pitch attitude angle isobtained from the results of the flying height measurement. The flyingheight is measured with a Dynamic Flying Height Tester made by PhaseMetrics, Inc. The flying heights of the edge on the air flow-in side andthe edge on the air flow-out side are measured using an ultra-smoothglass disk having a mean surface roughness Ra of 0.5 nm, and the pitchattitude angle Θ is obtained by the difference of the flying heights andthe distance between both measuring points.

As is shown by FIG. 5, when the pitch attitude angle decreases to notmore than 50 micro-radian, the vibration amplitude abruptly increases.This means that when the magnetic head slider begins to contact themagnetic disk at the edge on the air flow-in side, the vibrationamplitude will increase abruptly. Therefore, the pitch attitude anglemust be at least 30 micro-radian or more, and it is preferable for thepitch attitude angle to be 50 micro-radian or more from the standpointof reducing the vibration amplitude. As described, the configuration andpitch attitude angle of the magnetic head slider 1 affect the frictionforce, and therefore, affect the vibration amplitude strongly.

Similarly, the surface roughness and the form of the magnetic disk 10are measured with the scanning probe microscope of Digital Instruments,Inc. The measuring area was 20 μm-×20 μm. The measuring resolution inthe direction of height was 0.02 nm. The measured data was flatteningtreated by a two-stage filter before the analysis. As an index ofsurface roughness, adding to a generally used central surface roughness(mean surface roughness) Ra and maximum height Rp, peak counts areacquired simultaneously, since as the peak counts are found tosubstantially affect the vibration amplitude. The peak count is definedas the count of peaks exceeding a threshold level that is 1 nm above thecenterline of the surface roughness (mean surface roughness plane). Inother words, the peaks of the surface roughness exceeding the height of1 nm from the mean surface roughness plane are counted.

Each of the magnetic disks used for the experiments this time was asmooth disk having a mean surface roughness Ra of 1.5 nm and a glideheight of 6 nm. The method of obtaining the glide height is as follows.The flying height of the slider was measured beforehand as a function ofvelocity using a special slider provided with an Acoustic Emission (AE)sensor. On the magnetic disk, in order to measure the glide height, theslider is floated. From the velocity, where the output of the AE sensorincreases due to contact between the slider and the magnetic disk whenthe flying height is reduced by decreasing velocity gradually, the glideheight can be defined by an inverse operation (a flying height acquiredfrom the function between the flying height and the velocity).

There is a strong correlation among the mean surface roughness Ra, themaximum surface roughness height Rp and the glide height, and it iswidely known that to decrease the glide height, the surface roughnessmust be reduced. However, when the surface roughness is lower, thecontacting surface area is larger at the point of contact between themagnetic head slider and the magnetic disk, and the friction force willincrease, resulting in an increase in the vibration amplitude. Thisadversely affects the reliability of the magnetic disk deviceprofoundly.

To reduce the frequency of contact, a decrease of the glide height bysmoothing the surface roughness will be effective, but the smoothersurface will cause large vibrations when contact occurs, and, therefore,there is a contradictory request that surface roughness should not bemade smoother. However, the inventors have found that the difference ofpeak counts, that are the index of microscopic form of the surface ofthe magnetic disk, strongly affects the vibration amplitude at the pointof contact with a similar glide height as described below.

FIG. 6 is a diagram showing the relation between the peak count, that isthe index that shows the surface form of the magnetic disk 10, and thevibration amplitude. Disks providing the data shown in FIG. 6 areoperates with a glide height of 6 nm. The peak counts varied from250/400 μm² to 1600/400 μm².

As is shown by FIG. 6, the fewer the peak counts, the larger will be thevibration amplitude. On the other hand, the vibration amplitudedecreases with the peak count of 700 or more. When the peak count islower, the peak of the surface roughness is pushed down elastically bythe contact force exerted at the point of contact, and the magnetic headslider contacts the magnetic disk surface at the mean plane of thesurface roughness. Therefore, it is considered that the vibrationamplitude increases with the larger friction force produced by thelarger contacting surface. When the peak count exceeds a certain point,the many peaks of the surface roughness will share the contacting force,the deformation of the peaks of the surface roughness will be smallerand the increase of the contacting surface area will be prevented.Therefore, the friction force and the vibration amplitude are smaller.Though it could not be confirmed in the scope of the experiment at thistime, it is predicted that the excessive peak count will increase thecontacting area excessively and will increase the vibration amplitude.

As above described, a magnetic disk, used with a magnetic head sliderwhich operates the low flying height, that involves consideration ofcontact between the magnetic head slider and the magnetic disk, requiresconsideration of peak counts adding to the reduction of the conventionalsurface roughness index Ra and Rp for reducing the glide height. In thepreferred embodiment of the present invention, the peak count of 700/400μm² or more is desirable for reducing the vibration amplitude.

FIG. 7 shows a profile (calculated value) of the flying height of themagnetic head slider 1 over the whole surface of the magnetic diskoperating at ground altitude and at high altitude. The calculation iscarried out with a magnetic disk operating diameter of 65 mm (generallycalled 2.5 inch) and a spindle rotational speed of 4200 rpm. The averageflying height at ground altitude is approximately 10 nm, and a uniformfloating profile is realized over the whole surface of the magnetic disk(mainly by the effect of the depth d2 shown in FIG. 2). The decrease ofthe flying height at high altitude is 2 nm at the inner circumference ofthe magnetic disk and 1 nm at the outer circumference, and excellentfloating profile is realized at high altitude.

In this example, the average flying height is assumed to be 10 nm, butthe measured flying height of the mass-produced magnetic head slidervaries due to variation of the manufacturing techniques.

With the magnetic head slider of the preferred embodiment of the presentinvention, the variation of the flying height of ±2 nm and a decrease ofthe flying height of 1 nm of the magnetic head slider during a seekoperation are anticipated. Assuming the use of a smooth disk having aglide height of 6 nm, the magnetic head slider of the preferredembodiment of the present invention is assumed to contact the magneticdisk at the worst condition during operation at high altitude. Themagnetic head slider of the preferred embodiment of the presentinvention is designed, as will be described later, to minimize a drop inthe flying height during operation at high altitude.

As described above, the sub-ambient pressure force is large so that thevariation of the flying height produced by variation of themanufacturing tolerances is smaller than those of the conventionalcases. Therefore, in general, when the average flying height at groundaltitude is 15 nm or less, the contact between the magnetic head sliderand the magnetic disk must be considered at the worst condition.

FIG. 8 is a diagram showing the relation between the depth d1 betweenthe first surface and the second surface of the magnetic head slider 1and the vibration amplitude. The area of the first surface is very smallso that it does not significantly affect the floating force of themagnetic head slider. However, when the depth d1 is extremely shallow,such as 10 nm or less, the possibility of contacting the constitutingsurface 6 a of the second surface increases with contact between themagnetic head slider 1 and the magnetic disk 10. Therefore, the depth d1is preferred to be 10 nm or more.

Conversely, when the d1 is too deep, the surface 2 that represents theactual rail surface is separated from the surface of the magnetic disk,and the sub-ambient pressure force is diminished, causing an undesirablecondition with variation of the manufacturing tolerances and at thepoint of contact from the standpoint of stability. The depth d1 isdesirably in the range of 10 nm to 50 nm.

FIG. 9 is a diagram showing the relation between the depth d2 betweenthe second surface and the third surface of the magnetic head slider 1and the ratio of the maximum and minimum flying heights of the floatingprofile over the whole surface of the magnetic disk. The assumedcondition is similar to that of FIG. 7.

As described above, the depth d2 strongly affects to the uniformity ofthe floating profile. In an actual case, when d2 is 200 nm or more, thefloating ratio exceeds 1.2 and the uniform floating profile cannot bemaintained anymore. On the other hand, when d2 is extremely shallow, thefloating profile will be uniform, but the deviation of the flying heightdue to variation of the depth value of d2 will increase. Therefore, inthe preferred embodiment of the present invention, the depth d2 of 50 nmto 200 nm is preferable from the viewpoint of equalizing the floatingprofile and decreasing the fluctuation of the flying height. An adequatedepth d2 for equalizing the floating profile depends on the condition ofthe magnetic disk device. For example, in the case of a magnetic diskdevice having a 95 mm diameter (generally called a 3.5 inch) magneticdisk with a spindle rotational speed of 7200 rpm, the optimum depth d2is 150 nm to 400 nm.

FIG. 10 is a diagram showing the relation between the depth d3 betweenthe third surface and the fourth surface, and the decrease of the flyingheight at high altitude from the flying height at ground altitude.Generally, the decrease of the flying height at high altitude is moreconspicuous at the inner circumference of the magnetic disk, so that thedecrease of the flying height is measured at the inner circumference.The assumed condition is similar with that of FIG. 7.

FIG. 10 shows that the decrease of the flying height is minimum at thedepth d3 of 800 nm. When d3 is larger or smaller than this value, whichgives the minimum decrease of the flying height, the decrease of theflying height is larger. In the case of the magnetic disk device of thepreferred embodiment of the present invention, the depth d3 of 400 nm to1.3 μm is preferable. In other words, the position of the magnetic headslider relative the magnetic disk, referring to FIG. 3, is held at acertain flying height of the slider by effecting a balance between thesum of the slider suspension load W and the sub-ambient pressure forceN, which is exerted on the fourth surface having the depth d3, and thepositive pressure P, which is exerted on the slider.

If the sub-ambient pressure force does not change at high altitude fromthat of ground altitude in spite of the decrease in the positivepressure P at high altitude, the flying height of the slider dropsproportionally to the decrease of the positive pressure; however,actually, the sub-ambient pressure force drops at high altitude, and, ifthe level of the drop of the sub-ambient pressure force is similar tothe level of the drop of the positive pressure, similar floatingrelations are maintained both at high altitude and at ground altitude.

The depth d3, which maximizes the drop of the sub-ambient pressure forceto the level of the drop of the positive pressure, is 800 nm. That is,it has the characteristic of changing the sub-ambient pressure force bythe value of the depth d3. The optimum depth d3, which reduces the dropof the, flying height at high altitude, depends on the unit condition.For example, in the case of a magnetic disk device having a 95 mmdiameter magnetic disk, with a spindle rotational speed of 7200 rpm, anadequate depth d3 is 1 μm to 2.5 μm.

FIG. 11 is a diagram showing the relation between the area of the firstsurface constituting element 5 a of the magnetic head slider 1 and thevibration amplitude. It shows that the vibration amplitude increasesunilaterally with an increase of the area of the first surfaceconstituting element 5 a. Therefore, the area of the first surfaceconstituting element 5 a, which is the surface which comes into contactwith the magnetic disk, must be as small as possible. For example, tolimit the vibration amplitude to 1 μm or less, the area of the firstsurface constituting element 5 a is desirably 1000 nm² or less.

In the preferred embodiment of the present invention, the magnetic headslider comprises four substantially parallel surfaces; and, when thesurfaces are sequentially named from the surface nearest to the magneticdisk as a first surface, a second surface, a third surface and a fourthsurface, in a state wherein the magnetic head slider faces the magneticdisk, the magnetic head slider is constituted in such a way thatS1>S2>S3>S4, while the total area of the magnetic head slider existinginside the first surface is S1, the total area of the magnetic headslider existing inside the second surface is S2, the total area of themagnetic head slider existing inside the third surface is S3 and thetotal area of the magnetic head slider existing inside the fourthsurface is S4.

FIG. 12 shows an example of the process of producing the magnetic headslider of the present invention. Currently, as the base material of themagnetic head slider, sintered material, such as AlTiC, is generallyused.

As a surface finally facing the magnetic disk, a carbon protecting filmlayer 12 is provided for the main purpose of preventing the corrosion ofmagnetic head 9, and this film layer 12 is formed on a silicon layer 11,which is an adhesive layer. In the preferred embodiment of the presentinvention, the desired shape is formed by repeating Ar ion milling threetimes, as is shown in FIG. 12. At the final step, the silicon adhesivelayer 11 and the carbon protective layer 12 remain only on the firstsurface constituting element 5 a, which is mounted with the magnetichead, and on the first surface constituting elements 5 b and 5 c.

In the preferred embodiment of the present invention, the Ar ion millingis used as the method of processing, but the essential part of thepresent invention is not the method of processing; and, therefore, theshape can be formed with any kinds of processing method.

FIG. 13 is a top view of the magnetic head slider in accordance with asecond preferred embodiment of the present invention, and FIG. 14 is across section taken along line A—A in FIG. 13.

The difference between the magnetic head slider 1 of the secondpreferred embodiment of the present invention and the magnetic headslider of the first preferred embodiment of the present invention isthat the flow-in edge side of the first surface constituting element 5 aand the flow-out edge side of the first surface constituting elements 5b and 5 c are at the same depth as the fourth surface constitutingelement 8. By this preferred embodiment of the present invention, asthere is no third surface constituting element 7 a which is connected tothe first surface constituting element 5 a, the floating force generatedby the first surface constituting element 5 a can be decreased more thanthat of the first preferred embodiment of the present invention.

FIG. 15 is a top view of a magnetic head slider which constitutes athird preferred embodiment of the present invention. The first surfaceconstituting element 5 a and the second surface constituting element 6 aof the magnetic head slider of the third preferred embodiment of thepresent invention are not separated by the third surface constitutingelement 7 a, but are formed continuously. The area of the first surfaceconstituting element 5 a is made smaller to the extent that the size ofthe magnetic head 9 allows.

FIG. 16 is a top view of a magnetic head slider constituting a fourthpreferred embodiment of the present invention. Like the third preferredembodiment of the present invention, the size of the first surfaceconstituting element 5 a is made as small as possible, and the thirdsurface constituting element 7 a separates the first surfaceconstituting element 5 a from the second surface constituting element 6a.

FIG. 17 is a top view of a magnetic head slider constituting a fifthpreferred embodiment of the present invention. The shape of the magnetichead slider of the fifth preferred embodiment of the present inventionis similar to that of the first preferred embodiment of the presentinvention, but without provision of the first surface constitutingelements 5 b and 5 c positioned on the side the air flows in. While themagnetic head and the magnetic disk perform the recording and thereproduction while in contact, the first surface constituting elements 5b and 5 c are floating separately on the magnetic head, and so thesesurfaces are not related to the essence of the present invention.

FIG. 18 is a perspective view of the magnetic disk device 13 mountedwith the magnetic head slider, which is implemented by the first tofifth preferred embodiments of the present invention. This magnetic diskdevice is provided with a load/unload mechanism, and the magnetic headslider 1 stands by on a ramp 14 while the magnetic disk device isstopped. Only while the magnetic disk device is in operation will themagnetic head slider be loaded on the magnetic disk 10 and the recordingor the reproduction executed. Using the magnetic head slider of thispreferred embodiment of the present invention, the vibration of themagnetic head slider is not amplified by contact with the magnetic diskduring the recording or the reproduction operations, and stablerecording or reproduction can be continued for a long time.

FIG. 19 is a top view of a magnetic head slider constituting a sixthpreferred embodiment of the present invention.

The floating surface of the magnetic head slider of the first to fifthpreferred embodiments of the present invention comprises forsubstantially parallel surfaces, but the floating surface of themagnetic head slider of the sixth preferred embodiment of the presentinvention comprises three substantially parallel surfaces. That is, themagnetic head slider comprises surfaces 6 a, 6 b and 6 c which are railsurfaces, surfaces 7 a and 7 b which are step air bearing surfaces, andsurface 8 which is at the bottom of a recess for generating asub-ambient pressure force.

The feature of the sixth preferred embodiment of the present inventionis that the rail surface 6 a is formed to have a T-shape by thecombination of a long sideway rail part 15 which extends in thecrosswise direction of the slider and a lengthwise rail part 16 whichextends in the direction of the length. By such a configuration, thelong sideway rail part 15, being formed continuously from the step airbearing 7 a, generates a floating force and floats on the magnetic disk10. On the other hand, since the lengthwise rail part 16 is narrow andcannot generate enough floating force, the flow-out edge and thevicinity of the lengthwise rail part mounted with the magnetic head 9contacts the magnetic disk. Furthermore, the area of the lengthwise railpart is narrow so that the vibration amplitude at the contact point withthe magnetic disk can be kept smaller.

The contacting part of the magnetic head slider of this preferredembodiment of the present invention is not separated three dimensionallycompared with those of the first to fifth preferred embodiment of thepresent invention, and, if the vibration amplitude happens to beenlarged, there is a possibility of the danger that the long sidewaysrail part 15 will contact the magnetic disk. However, there is theadvantage that the ion milling steps can be reduced by one step comparedto those of the first and second preferred embodiment of the presentinvention, since the long sideways rail part 15 and the lengthwise railpart 16 are on the same plane.

The center rail shape of the magnetic head slider of the sixth preferredembodiment of the present invention can be formed by not only an ionmilling process, but also by the Focus Ion Beam (FIB) process. The FIBprocess is frequently used for forming the track width of the magnetichead with a high precision.

The lengthwise rail part 16 of the sixth preferred embodiment of thepresent invention can also be formed by forming the flow-out edge sideof the rail surface 6 a during the forming of the track width. In thiscase, a step difference, of which depth is different from that of thestep air bearing 7 a formed by ion milling, is formed around thelengthwise rail part 16.

FIG. 20 is a top view of a magnetic head slider constituting a seventhpreferred embodiment of the present invention.

The floating surface 4 of the magnetic head slider of the seventhpreferred embodiment of the present invention comprises threesubstantially parallel surfaces similar to that of the sixth preferredembodiment of the present invention. However, in contrast to the sixthpreferred embodiment of the present invention, the step air bearing 7 aseparates the long sideways rail part 15 from a contact pad 17.

Both with the sixth and seventh preferred embodiments of the presentinvention, it is important for decreasing the vibration amplitude thatthe area of the rail part near the element part contacting the magneticdisk, comprising the lengthwise rail part 16 and the contact pad 17, isnarrower than the area of the long sideways rail part 15 which generatesthe floating force.

As described above, the present invention has the effect of maintaininghigh reliability by equalizing the flying height over the whole surfaceof the magnetic disk and of reducing the change of the flying heightproduced by variation of the processing, during the seek operation andduring operation at high altitude, so that the magnetic head will slideon the surface of the magnetic disk smoothly at the contact pointbetween the magnetic head and the magnetic disk.

What is claimed is:
 1. A magnetic disk device comprising: a magneticdisk; a magnetic head slider with a magnetic head mounted thereon andhaving a first surface, a second surface, a third surface and a fourthsurface which are formed sequentially from an adjacent side to saidmagnetic disk, and a gap of said magnetic head being arranged on saidfirst surface; wherein a relation of d1<d2<d3 is established, where saidd1 is a depth from said first surface to said second surface, said d2 isa depth from said second surface to said third surface, and said d3 is adepth from said third surface to said fourth surface; and wherein saidmagnetic head slider has a floating pitch attitude of at least 50micro-radians with respect to said magnetic disk.
 2. A magnetic diskdevice as claimed in claim 1, wherein said d1 is 10 nm to 50 nm, said d2is 50 nm to 200 nm, and said d3 is 400 nm to 1.3 μm.
 3. A magnetic diskdevice as claimed in claim 1, wherein a total area of said first surfaceis smaller than a total area of other of said surfaces.
 4. A magneticdisk device as claimed in claim 1, wherein a relation of S1<S2<S3<S4 isestablished, where a total area of said first surface is said S1, atotal area of said second surface is said S2, a total area of said thirdsurface is said S3, and a total area of said fourth surface is said S4.5. A magnetic disk device as claimed in claim 1, wherein said firstsurface is formed with a protective coating made of a carbon film.
 6. Amagnetic disk device as claimed in claim 1, wherein said first surfaceis surrounded by said fourth surface.
 7. A magnetic disk devicecomprising: a magnetic disk; a magnetic head slider with a magnetic headmounted thereon and having a first surface, a second surface, a thirdsurface and a fourth surface which are formed sequentially from anadjacent side to said magnetic disk, and a gap of a magnetic head beingarranged on said first surface; wherein a relation of d1<d2<d3 isestablished, where said d1 is a depth from said first surface to saidsecond surface, said d2 is a depth from said second surface to saidthird surface, and said d3 is a depth from said third surface to saidfourth surface; wherein a part of said second surface, is arranged nearan air flow-out edge and comprises a long sideways rail surface on anair flow-in side and a lengthwise rail surface on an air flow-out side;and wherein said magnetic head slider has a floating pitch attitudeangle of at least 50 micro-radians with respect to said magnetic disk.8. A magnetic disk device as claimed in claim 7, wherein in an area ofsaid long sideways rail surface is larger than an area of saidlengthwise rail surface.